Gas condensing boilers – technology for different needs

When it comes to convenient heat generation with natural gas, Viessmann offers various technologies for all kinds of demands and situations. The product range includes gas heating systems for new and existing buildings as well as for owner-occupied apartments and detached houses. Large-scale projects in the housing, commercial and municipal sectors can also be implemented.

Compact boilers are space saving wonders

Wall mounted gas condensing boilers are particularly suitable for use in new buildings and small apartments. These extremely compact appliances can fit in virtually any space. They are used either solely for DHW heating or for space heating as well. In the case of the latter, they are referred to as combi boilers. Both versions work according to the instantaneous water heating principle. They therefore do not usually have a storage water heater and only heat water when it is needed. This means that they react very quickly to changing requirements. The disadvantage of DHW heating using the instantaneous water heating principle is that hot water is not available immediately. To avoid having to run water from the tap for a long time before it gets hot, some wall mounted gas condensing boilers have a small integral storage water heater.   

Floorstanding gas condensing boilers for greater efficiency with high DHW demand

Floorstanding gas condensing boilers take up slightly more space. This is mainly because they have a larger storage water heater in which the heated DHW is kept at a constant temperature for a longer period of time. This is particularly efficient if larger quantities are needed on a regular basis.

If there are plans to connect a solar thermal system for DHW heating, we recommend choosing a floorstanding gas condensing boiler with integral solar indirect coil. This is mounted on the buffer cylinder or near the draw-off point and heats the DHW. In combined systems such as these, there is no mixing of heating water and DHW. The floorstanding units are already designed for dual mode operation. This means that they can easily be combined with another heat generator to cover the heat demand. In terms of technology, Viessmann gas condensing boilers are state of the art and cover an output range of around two to 100 kilowatts (kW). This enables them to efficiently and reliably supply heat to detached homes, two-family houses and small apartment buildings at all times.

Floorstanding gas condensing boilers are also available in larger sizes. These are mainly used in buildings with a high heat demand, typically apartment complexes, public buildings and commercial premises. Thanks to the cascade function, several appliances can be quickly connected to form one unit and provide reliable heat in this area too. 

Combining climate protection and financial relief

Vitodens 343-F gas condensing boiler

In Germany alone, there are still around two million heating systems in use today that are more than 25  years old. By replacing these boilers with highly efficient gas condensing boilers, consumers can save a lot of energy –– as much as 35  percent when a modern gas heating system is used alongside solar technology. This would translate into ten percent of Germany's total energy needs, with annual CO₂ emissions being reduced by up to 54  million tonnes at the same time.

The savings are made possible because condensing technology uses energy extremely efficiently. This is due to the fact that it converts virtually all of the energy content of a fuel into heat. So anyone opting for a gas condensing boiler, for example, is able to keep their heating costs low in the long term while reducing the burden on the environment. After all, less combustion also means fewer CO₂ emissions.

All Viessmann gas condensing boilers meet EU-wide requirements for efficient condensing technology. 98  percent or more of the energy spent is converted into heat. With such unbeatably high levels of efficiency, anyone opting for one of these gas heating systems is making a positive contribution to protecting the climate and the environment.

How gas heating with condensing technology works

As already mentioned, condensing technology uses energy very efficiently. It not only utilises the heat generated by combustion as a measurable temperature of the hot gases (net calorific value), but also the water vapour content (gross calorific value). This contains "latent" heat, which in older heating systems is discharged to the open air via the chimney. This latent heat can be recovered by passing the flue gases produced during combustion through a heat exchanger until the water vapour contained in the gases condenses. The condensation process produces thermal energy which is then used to preheat the heating water.

Viessmann Vitodens 200-W wall mounted gas condensing boiler

Futureproof, reliable heating technology is here now

Calls for resource-saving heating technologies are growing ever louder. New gas condensing boilers should not only work cleanly, but also sustainably. In response, Viessmann has already been futureproofing its gas condensing heating systems. Thanks to their combustion controller, these boilers adjust automatically to various gas types – including biogas mixtures. Furthermore, the products are currently suitable for use with natural gas/hydrogen blends containing up to 20 percent hydrogen. However, we would like to increase this proportion still further.


100 % hydrogen operation planned from 2025

Find out more about Viessmann "H2 ready" heating appliances.

The benefits of wall mounted and floorstanding gas condensing boilers 

Condensing technology is now the benchmark for new gas heating systems. System owners opting for this technology benefit from numerous advantages:

Energy contained in the fuel is converted into heat with virtually no losses
Efficient combustion reduces heating costs and CO₂ emissions
Proven technology ensures high operational reliability and reduces risk of unexpected failures
Option to combine with renewable heating systems
State subsidies for a combination with renewable energies reduce purchasing costs

Choosing a gas condensing heating system also means there's no need for a fuel store in the house. If there is a gas connection available, no tank is required. The compact gas condensing boilers are also space saving.

House with Viessmann gas condensing boiler in the basement and solar thermal system on the roof

Easy to combine with renewable heating systems

As already mentioned at the beginning, one of the advantages of gas condensing technology is its high level of compatibility. In practice, this means that most gas condensing boilers come from the factory already prepared for combined operation. The combination of gas condensing boiler and solar thermal system has proven to be very ecological and economical. In this configuration, the solar thermal system is responsible for DHW heating using the free solar energy. This means that the gas boiler does not have to do so much work. This also reduces heating costs.

To the solar thermal system product range

Combining with a heat pump is another possibility. In this dual mode operation, the heat pump not only provides domestic hot water the whole year round, but also heating. If peak loads occur when the weather is very cold, the gas boiler is switched on as well.

It is also possible to operate a gas condensing boiler with a biomass heating system. Be it a log boiler, pellet boiler or woodchip boiler: here too, the gas boiler only needs to be switched on if there is an unexpectedly high heat demand.

*Manufacturer's declaration of convertibility to 100 % hydrogen in accordance with the Gebäudeenergiegesetz (GEG) at

Product range

Whether it be gas condensing boilers, floorstanding units with integral solar indirect coil or cascadable heating appliances for high heat demands, Viessmann can offer the right gas condensing heating system for a wide range of needs.


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